The present invention relates to an optical head and an optical disk using the same for recording or playing back information to and from an optical information medium such as an optical disk. More specifically, the present invention relates to an optical head and an optical disk using the same that can record information using a laser module in which multiple semiconductor laser chips having different wavelengths are mounted.
In optical information recording/playback devices such as optical disk devices, various features are desired in addition to a compact and thin design.
For example, there is a significant demand for using a single compact optical head that can record and playback both CD-R (Compact Disk-Recordable), which has seen widespread use as a writable optical disk medium, and DVD-RAM (Digital Versatile Disc/Digital Video Disc), which was developed recently as an optical disk medium allowing high-density recording. The wavelength of lasers used in recording and playback of CD-Rs is approximately 780 nm, while the wavelength of lasers used in recording and playback of DVDs is approximately 660 nm. Thus, there is a need to mount both a laser light source with a 780 nm wavelength and a laser light source with a 660 nm wavelength on a single optical head.
For example, Japanese laid-open patent publication number Hei 10-261240 and Japanese laid-open patent publication number Hei 10-289468 propose a compact optical head which integrates into a single unit a semiconductor laser chip with a wavelength of approximately 780 nm for CDs, a semiconductor laser chip with a wavelength of approximately 660 nm-for DVDs, and an optical detector element.
Laser beams emitted from light-emitting points at different positions generally pass through different positions of a lens system at different angles. In these optical heads, the laser beams emitted from the two semiconductor laser chips enter a focus lens at different positions and different angles. In the embodiments described in Japanese laid-open patent publication number Hei 10-261240 and Japanese laid-open patent publication number Hei 10-289468, a semiconductor laser chip with a 660 nm wavelength for DVDs is disposed on the optical axis of a lens system formed by a focus lens and a collimating lens. A semiconductor laser chip with a 780 nm wavelength for CDs is disposed away from the optical axis of the lens system. Since the laser beam for DVDs enters the focus lens directly from above, the DVD laser spotlight does not tend to generate aberration. On the other hand, the laser beam for CDs enters the focus lens at an angle, and therefore tends to generate aberration (especially coma aberration) in the laser spotlight for CDs.
In Japanese laid-open patent publication number Hei 10-261240, a holographic optical element is used. In Japanese laid-open patent publication number Hei 10-289468, an optical means using polarizing prism (a birefringent plate) or holograms allows just the optical path of the laser beam for CDs to be bent so that it enters straight into the focus lens.
To record information, there is also the need for beam-shaping means to take a laser beam with anisotropic optical intensity distribution emitted by a semiconductor laser and efficiently focus it to an optical spot that has an isotropic optical intensity distribution.
Furthermore, there is a great demand for compact design in optical heads. Although not described in the embodiments in Japanese laid-open patent publication number Hei 10-261240 and Japanese laid-open patent publication number Hei 10-289468, this generally requires optical components other than the focus lens to be arranged on a plane parallel to the disk surface and an upward projecting mirror to guide the beam to the focus lens.